The integrated circuits produced in SOI technology offer a certain number of advantages. Such circuits generally exhibit a lower electrical consumption for equivalent performance levels. Such circuits also induce lower stray capacitances, so that the switching speed can be improved. Furthermore, the stray triggering (“latchup”) phenomenon encountered with MOS transistors in bulk technology can be avoided. Such circuits therefore prove particularly suited to applications of SoC or MEMS type. It is also found that the SOI integrated circuits are less sensitive to the effects of ionizing radiation and thus prove more reliable in applications where such radiations can induce operating problems, notably in space applications. The SOI integrated circuits may notably include random access memories of SRAM type or logic gates.
Reducing the steady-state consumption of logic gates while increasing their switching speed is the subject of a great deal of research. Some integrated circuits being developed incorporate both logic gates with low consumption and logic gates with high switching speed. To generate these two types of logic gates on one and the same integrated circuit, the threshold voltage of certain transistors of the fast-access logic gates is lowered, and the threshold voltage of other transistors of the logic gates with low consumption is increased. In bulk technology, the modulation of the threshold voltage level of transistors of the same type is performed by differentiating the level of doping of their channel. However, in FDSOI (“Fully Depleted Silicon On Insulator”) technology, the doping of the channel is almost zero (1015 cm−3). Thus, the level of doping of the channel of the transistors cannot therefore exhibit significant variations, which prevents the threshold voltages from being differentiated in this way. One solution proposed in certain studies for producing transistors of the same type with distinct threshold voltages is to incorporate different gate materials for these transistors. However, the practical production of such an integrated circuit proves technically difficult and economically prohibitive.